Imaging techniques such as computed tomography are often used to aid in directing the insertion of one or more probes into the patient's body during percutaneous biopsies and other similar procedures (e.g., hyperthermia probes, radiation seeds, etc.). In CT aided biopsies, a scan is typically obtained to visualize the lesion to be biopsied. Using the image generated during the scan, the target site and the entry point on the patient's skin are selected and marked on the CRT screen. The computer then calculates the distance and the angle of the insertion in order to reach the target site and displays the biopsy path on the screen.
The entry point is then marked on the patient's skin and the needle or probe is advanced into the patient's skin and tissues under free-hand control by the physician. Because of anatomy and overlying structures, the path selected for entry of the needle or probe is often not vertical but rather at an angle to the vertical. Often times a compound angle--that is, an angle with respect to the vertical in both the sagittal plane (i.e., the plane extending from head to toe) and the axial plane (i.e., the plane extending across the body from one side to the other)--must be used in order to avoid penetrating areas such as vital organs.
Although such procedures may be performed using a free-hand technique, it is difficult to ensure sufficient accuracy in orienting and maintaining the needle at the correct angle. The free-hand technique is even less precise and even more difficult when a compound angle is used. For example, in deep biopsies, even a few degrees deviation in angulation will result in a significant error in needle position. This can have undesirable consequences when the target lesion (e.g., tumor) is small and the path is close to surrounding vital structures, such as the aorta and nerves.
One approach taken in the past to increase the accuracy of needle orientation is the use of device to physically constrain the needle so that its path conforms to the predetermined path, for example, such as that used in stereotaxis guidance systems. One such device is disclosed in U.S. Pat. No. 4,583,538 (Onik et al.). Unfortunately, this approach has several drawbacks. First, since the guidance device touches the needle, it must be sterilized prior to use. Second, and perhaps more importantly, the physician loses some degree of control and feel over the needle placement. The tactile sensation of the user is an essential element in the control of needle placement. Guides which physically constrain the needle necessarily compromise tactile needle control by the user. Lastly, setting the desired angulation is often a difficult and time consuming process in such devices and involves making various complex calculations.
Another approach involves the use of a light beam or laser as a guide so that the needle is not touched or physically constrained. In one such approach, two intersecting beams of light are used to guide the needle placement, see, for example, U.S. Pat. No. 4,651,732 (Frederick). Unfortunately, such systems required two light sources and, thereby, increase the complexity of the device and its use. In another approach, a computer and a raster driven light source connected to a C-arm are used to generate a laser beam onto the patient, see, for example, Nagata et al., "Laser Projection System for Radiotherapy and CT-Guided Biopsy," Journal of Computer Assisted Tomography, vol. 14, no. 6, p. 1046-1048 (1990). However, such systems are quite complex and, accordingly, expensive and have not entered into routine clinical practice for biopsies. In addition, the characteristics of such devices may limit the range of compound angles. Also, its physical mass can be in the way in certain biopsy situations.
Further, probes for use in biopsies typically employ a stylet that slides within a hollow needle. In order to force the stylet into the tissue and guide its path, the needle must be firmly grasped along its length. However, such grasping can cause the probe to deflect. Although enlarged hubs have been developed that allow the needle to be more firmly grasped, one must typically insert a finger over the rear end of the stylet in order to prevent its tip from retracting into the needle, thereby complicating the guiding and insertion of the stylet.
Consequently, it would be desirable to provide an apparatus for performing biopsies and the like using a free-hand technique, with a light beam as a guide, capable of accurately and firmly directing the beam at an angle and yet that is easy to use and readily adjustable over a wide range of angles. It would be further desirable to provide a probe that facilitated such a light beam guided, free-hand technique.